Method and apparatus for enhancing relay life
US5530615A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Dec 6, 1993 |
| Grant date | Jun 25, 1996 |
| Priority date | — |
| Expiry date | Dec 6, 2013 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH01H2009/566
- WIPO fieldElectrical machinery, apparatus, energy
- WIPO sectorElectrical engineering
Abstract
An electronic control for gas furnaces controls a two speed main blower fan and an induction draft fan based on 24 volt input signals from a room thermostat, a high limit and an ignition control including a gas valve. The input signals are coupled to input ports of a microprocessor through current limiting resistors and to AC ground through pull down resistors. AC ground is also connected to the IRQ port of the microprocessor. Output ports of the microprocessor are connected to a relay driver which in turn is connected to relays for energizing and de-energizing the fans. The control calibrates itself on a continuing periodic basis to read the AC inputs synchronously at the peak of their wave and can switch the relays asynchronously based on the Real Time Clock of the microprocessor or can be switched synchronously by providing a selected delay so that contact engagement and disengagement occurs at or near the zero crossing of the AC line voltage wave form. When used with resistive loads the relays are switch in response to a signal from the microprocessor which is delayed based on the mechanical switching time constant of the relays to provide contact closure and opening at the sel…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.